Tube support system

ABSTRACT

A vapor generating apparatus having an evaporator section, a portion thereof including the wall tubes forming an upright gas passage and the support tubes supporting the heat exchanger surface suspended within said gas passage.

United States Patent [191 Franzmann et a1.

[ TUBE SUPPORT SYSTEM [75] inventors: Karl Franzmnnn; Paiil Schleiiier,

both of Oberhausen, Germany [73] Assignee: Babcoclr & Wilcox Limited, London,

England [22] Filed: Nov. 24, 1971 [21] App]. No.: 201,905

[52] US. Cl. 122/510 [51] F22b 37/24 [58] Field of Search 122/6 A, 478, 510

[56] References Cited UNITED STATES PATENTS 3,003,480- 10/1961 Fink et a1 122/510 [11] 3,754,533 [451 Aug. 28. 1973 3,060,909 10/1962 Ott 122/510 3,307,523 3/1967 Palchik et a1. 122/510 X 3,368,536 2/1968 Sullivan 122/510 Primary Examiner-Kenneth W. Sprague Attorney-J. Maguire [57] ABSTRACT A vapor generating apparatus having an evaporator section, a portion thereof including the wall tubes forming an upright gas passage and the support tubes supporting the heat exchanger surface suspended within said gas passage.

2 Claims, 3 Drawing Figures Pmtmimucza ma INVENTQR.

' Karl .Franzmann Paul Schleuier V I AT i ORNE-X TUBE SUPPORT SYSTEM BACKGROUND OF THE INVENTION particularly,

The invention relates generally to vapor generating and superheating units of the type which are topsupported and include heat exchange surface suspended within and'terminating outside of the gas pass enclosure. More particularly the invention is directed at an arrangement for supporting the heat exchange surface, and allowing its terminal portions to'be rigidly connected to the gas pass enclosure while eliminating stresses due to thermal expansion.

The gas pass enclosure of a conventional vapor generating and superheating unit includes an upright furnace chamber defined by a gas tight tubular wall structure having its lower portion forming a combustion space and its upper portion housing tubular heat exchange surface such as a superheater, reheater and/or economizer which have their tube ends extending through the wall structure for connection to headers and associated control elements situated'outside of the gas pass enclosure.

The furnace wall structure'is formed with spaced parallel tubes having substantially all of their intertube spacing closed by metallic webs which are seal-welded to the tubes. While, in order to maintain gas-tight integrity, the heat exchanger tubeends which penetrate the wall structure are seal-welded thereto at the point of penetration.

The rigid attachment resulting from seal-welding the penetrating tube ends to the wall structure dictates that the suspended heat exchange surface be capable of readily adjusting'to the downward movement imposed on its tube ends asa result of thermally induced growth of the furnace wall structure. If this were not the case, and should a differential in thermal expansion occur between the tube ends and the adjoining wall structure, the resultant restraint on movement would give rise to stresses which may eventually cause failure of the gastight closure and/or the adjoining tube surfaces.

SUMMARYVOF THE INVENTION The present invention provides a heat exchanger support arrangement which functions at substantially the same operating temperature as the surrounding wall structure. This is achieved through a novel support arrangement fonned of generally upright tubes having a fluid flow circuitry which is parallel to that of the surrounding wall structure.

Accordingly, the tubes forming the surrounding wall structure and those forming the heat exchanger support arrangement are supplied from and. discharged into the same or equivalent headers. In the fluid flow circuitry of a typical vapor generator the fluid supply source for the support and surrounding wall tubes will be generally situated at an intermediate point along the evaporator section and thefluid discharge point will coincide with the end of the evaporator section. The heating fluid being conveyed through these tubes will be a steam-water mixture of increasing quality as it approaches the discharge point and its flow will be substantially parallel and in the same direction. The parallel circuitry results in equality of pressure distribution and therefore in equality of phase temperature within the respective wall and support tubes. Consequently, the operating metal temperatures of the wall and support tubes will be substantially the same for a given load and will have substantially equal rates of thermally-induced growth.

In the case where the construction of the vapor generator requires that there be support tubes both inside and outside of the gas pass enclosure, the operating metal temperature of both the inside and outside support tubes will remain substantially the same for any given load, inasmuch as the metal temperature of the inside tubes is governed by the boiling point of the water within the tubes and the metal temperature of the outside tubes is governed by the condensation point of the saturated steam within the tubes, with both the boiling and condensation points being at the same temperature.

The fluid flow circuitry of a typical vapor generator will include a steam-water separating section flowconnected to the discharge end of the evaporator section. In the case where the construction of the vapor generator requires that the evaporator section be sub divided into several fluid flow circuits, there is provided a separate steam-water separator at the end of each of the flow circuit subdivisions. The support tubes will also be subdivided into flow circuits parallel to those of the evaporator section, with the number of subdivisions being equal to the number of steam-water separators.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a section of a top-supported forced flow once-through steam generating and superheating unit for central station use. There is shown a gas pass. enclosure includingan upright furnace chamber of substantially rectangular horizontal cross-section havingits lower portion forming a combustion space 10 -defined by the wall tubes 14 and its upper portion forming a gas passage 12 defined by the wall tubes 16. The .up-. right boundary walls are formed as a gas tight construction by extending the tubes in spaced parallel fashion and having all of their intertube spacing closed by me: tallic webs.

The vapor generator is top-supported by structural steel members including upright columns 18 and cross beams 20, and is supportingly attached to the structural steel through a plurality of hangers 22 some of which are connected to the support and wall tubes as shown in the drawing. During operation of the unit, the thein mally-induced metal growth will cause the wall tubes 14 and 16, the support tubes 24 and 26, and the components attached thereto and/or suspended therefrom to move in a downward direction relative to the support point at the hangers 22.

The furnace tube wall structure is arranged in panels coplanar with the respective walls and is associated with a group of lower headers, not shown, supplying fluidto the wall structure and a group of intermediate headers 28 and 30 for mixing the fluid at an intermediate level along the wall structure and a group of upper headers 32 and 34 for discharging the fluid from the wall structure.

With reference to FIGS. 1 and 2, the upper ends of tubes 14 of the front and rear walls of the combustion space discharge through the intermediate headers 28 into the tubes 16 of the front and rear walls of gas passage 12 which in turn discharge through the upper headers 32. The tubes 14 of the sidewalls of the combustion space 10 discharge through the intermediate headers 30 into the tubes 16 of the sidewalls of gas passage 12 which in turn discharge through the upper headers 34.

The gas passage 12 contains heat exchangers such as that shown at 36, 38 and 40; these may respectively represent the secondary superheat, reheat and primary superheat surfaces. The heat exchanger 36 is supplied through headers 42 and discharges through headers 44 while the heat exchanger 38 is supplied through headers 46 and discharges through headers 48 and the heat exchanger 40 is supplied through headers, not shown, and discharges through headers 50. The heat exchangers 36, 38 and 40 have their end portions passing between the rows of front and rear wall tubes 16 for connection to their respective inlet and outlet headers, all of which are located outside of the gas passage 12. The heat exchanger end portions extending through the wall structure are seal welded to the metallic web covering the wall intertube spacing.

in accordance with the invention, the heat exchangers 36, 38 and 40 and their respective inlet and outlet headers and associated control components are supported by the tubes 24 which are disposed inside the gas passage 12 and the tubes 26 which are disposed outside of the gas passage 12. In a typical arrangement the support tubes 24 and 26 may be provided with saddle lugs shaped to accommodate the heat exchanger tubes resting thereon. The headers associated with the heat exchangers may be resting on platforms as shown at 52 which are in turn supported by the adjoining support and wall tubes 26 and 16, respectively. The support tubes 24 and 26 are themselves supported from the structural steel through the hangers 22. Fluid is supplied to the support tubes 24 and 26 through the headers 28. and is discharged through the headers 54.

The fluid discharging from each of the headers 32, 34 and 54 is conveyed to a respective steam-water separator 56. A transition piece such as shown at 55 maybe utilized to flow connect the headers 32 to the steamwater separators 56.

FIG. 3 shows an intermediate header 28 associated with the rear wallof the gas passage 12 and supplying the support tubes 24, the latter have portions thereof bifurcated as shown at 64 to accommodate the supporting of the tubes associated with the heat exchangers 36, 38 and 40. The, support tubes 24 are in turn suspended from hangers 22 for support by the structural steel, the latter being the means for top-supporting the vapor generator.

In the normal operation of the vapor generating unit, the combustion cycle includes conveying the flue gases through the furnace chamber to heat the fluid passing through the wall tubes 14 and 16, the support tubes 24 and the heat exchangers 36, 38 and 40. The flue gases are thereafter discharged through a tube screened outlet 58, located in the rear wall of gas passage 12, for flow through a gas passage 60, the latter including a damper arrangement 62 for regulating the furnace draft or pressure.

The fluid cycle includes supplying feedwater at high pressure for passage through the economizer section and for heating therein, thereafter conveying the heated feedwater to the evaporator section wherein additional heat is absorbed and the feedwater undergoes a phase change resulting in a very high quality steamwater mixture being discharged from the evaporator section. The evaporator section comprises the support tubes 24 and 26 and the wall tubes 14 and 16 which define the combustion space 10 and gas passage 12, respectively. Heated feedwater is supplied through headers, not shown, located at or near the bottom of the combustion pass 10, and is conveyed through the wall tubes 14 wherein it absorbs sufficient heat from the combustion gases to undergo a phase change into a steam-water mixture before entering the intermediate headers 28 and 30 which supply the wall tubes 16 of gas passage 12 and the support tubes 24 and 26. The inter mediate headers 28 and 30 are also known as mix headers since they afford a re-mixing of the steam-water mixture exiting from the wall tubes 14 resulting in a steam-water mixture having a more homogeneous degree of quality. The fluid passing upwardly through the evaporator section remains substantially a steam-water mixture and maintains substantially the same temperature while absorbing heat to raise its steam quality. Thus, the temperature of the steam-water mixture passing through the support tubes 24 and 26 is substantially the same as the temperature of the steam-water mixture passing through the wall tubes 16. The metal temperature of the support tubes 24 and 26 and the wall tubes 16 corresponds closely to the temperature of the steam-water mixture passing therethrough and will thus be substantially the same for all of the tubes 16, 24 and 26. Consequently, the downward expansion due to thermally-induced growth will be the same for the wall tubes 16 as for the support tubes 24 and 26 at a given level, e.g., any one of the levels at which the tube ends of heat exchangers 26, 28 and 40 penetrate through the wall structure to connect to their respective headers. It follows that since the heat exchangers 36, 38 and 40 are supported by the support tubes 24 and the headers 42, 44, 46, 48 and 50 are supported by the wall tubes 16 and the support tubes 26, the downward movement of the heat exchangers and associated headers will be substantially the same as that of the supporting tubes 16, 24 and 26 at a given level and a rigid tie between components thereof such as the welding of heat exchanger tube end portions to the intertube web of the wall tubes 16 will not give rise to stresses due to thermal expansion.

The flow circuitry of the gas pass enclosure and the support tube arrangement may be subdivided into a plurality of parallel circuits. In the steam generating unit shown in the drawings, the support tube structure and the wall structure of the gas pass 12 are subdivided into four parallel fluid flow circuits, each discharging into a separate steam-water separator 56. The support tubes 24 and 26 discharge the steam-water mixture through the upper headers 54 to respective steamwater separators 56. The wall tubes 16 of the sidewalls of gas passage 12 discharge the steam-water mixture through the upper headers 34 and through the transition pieces 55 to the steam-water separators 56. The wall tubes 16 of the front and rear walls of the gas passage l2 discharge the steam-water mixture through the upper headers 32 to the steam-water separators 56. The separators 56 separate the residual water from the high quality steam with the former being recycled back to the feedwater system and the latter being conveyed through to the superheaters such as that shown at 40 and 36.

While in accordance with the provisions of the statutes there is illustrated and described herein a specific embodiment of the invention, those skilled in the art will understand that changes may be made in the form of the invention covered by the claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of the other features.

We claim:

1. In a vapor generating apparatus having an evaporator section, the combination of:

' a substantially gas-tight tubular wall structure defining an upright gas passage,

at least one generally upright tubular heat exchanger suspended within the passage,

said heat exchanger having its end portions extending through the wall structure and outside of the passage, and

an arrangement for supporting the heat exchanger including a plurality of upright support tubes wherein some of the support tubes are disposed within the gas passage and the remainder are disposed outside of the gas passage,

said support tubes and said wall structure tubes forming a portion of the evaporator section,

header means for introducing a fluid for parallel flow through the support and wall structure tubes and header means for discharging said fluid therefrom.

2. In an apparatus according to claim 1 wherein at least some of said support tubes disposed within the gas passage are formed with bifurcated segments. 

1. In a vapor generating apparatus having an evaporator section, the combination of: a substantially gas-tight tubular wall structure defining an upright gas passage, at least one generally upright tubular heat exchanger suspended within the passage, said heat exchanger having its end portions extending through the wall structure and outside of the passage, and an arrangement for supporting the heat exchanger including a plurality of upright support tubes wherein some of the support tubes are disposed within the gas passage and the remainder are disposed outside of the gas passage, said support tubes and said wall structure tubes forming a portion of the evaporator section, header means for introducing a fluid for parallel flow through the support and wall structure tubes and header means for discharging said fluid therefrom.
 2. In an apparatus according to claim 1 wherein at least some of said support tubes disposed within the gas passage are formed with bifurcated segments. 